The results are interesting to put it mildly, we rely on our own data now and more
or less ignore manufacturers figures. This is particularly the case where they only
give a (peak) gain reading. Even if the latter is accurate, this figure can be misleading,
especially with wideband aerials. What you really want is the gain graph, but many
manufacturers won`t release this information, arrogant gits. Also see Aerial Polar
Diagrams.

Differences in the test results of one dBμV on any individual frequency should be
disregarded, manufacturing tolerances or a truck going over a hill somewhere between
the test site and the TX could easily account for those ! Furthermore the response
of any aerial is not linear, its gain curve will have bumps and dips in it. That
said, a 1dB difference across the whole bandis significant, and an increase (or
decrease) of two or three dB is very significant. It should be remembered that 3dB
is a 40% higher signal level, and such an increase at the aerial (as opposed to through
an amplifier) is very difficult to achieve. Obviously if you live in a decent reception
area these amounts of signal variation are not important, but if that`s the case,
you should just use a Log Periodic anyway !

On the left is Ferrybridge power station and on the right we have West Burton. Belmont
is situated just to the left of the latter, except it`s a further 26 miles away.....
From the test site you used to be able to see an incredible 7 (seven ! ) power stations,
these are marked with white pins on our TX map. Unfortunately, as of summer 2012,
that`s now down to five due to the cooling towers at Thorpe Marsh and High Marnham
being demolished. From the NE to the SE they are/were :

In order to give some idea of the gain of the tested aerials we also included in
the tests a 46 element (it`s actually a 28 element....) Tri Boom Yagi which is very
similar in performance to a DAT45. We do not stock Tri Booms (personally I think
they`re overrated) but for those who know of them, the figures could be illuminating.
I didn`t test the DAT 75 because it was too unwieldy, but Televes report it as being
about the same as a DAT 45 at CH 21, rising to +1dB at 45 and peaking at +2dB by
CH 62. Incidentally this trend for extra directors to add gain at the top end of
a widebands gain curve (and less so at the bottom) was reflected in our own tests
of other antennas.

It should be borne in mind that gain is not everything, which is why Logs are still
one of the best aerials despite being having relatively low gain figures. Impulse
noise rejection, directivity, out of band rejection, cross polar rejection and front
to back ratio and can all have significant effects on the quality of the received
signal. Having said that, gain is a function of the others (apart from impulse noise
rejection) as it demonstrates that the antenna is performing efficiently. Indeed
gain must be a function of the others. Why must ? Well an aerial is a passive device,
the only way it can increase its gain in a particular direction is at the "expense"
of gain in the other directions. As an aerial`s gain increases, its acceptance angle
(and its cross polar rejection come to that) decrease. They must do, there is no
other way for the aerial to increase its gain.

Finally, all of the above is before you even start talking about wind loading considerations
and/or build quality. Fortunately, we definitely know what we`re talking about when
it comes to the latter, there are no “Bacofoil” aerials here......

This table compares six Yagi 18s of the samemodel, but of all five groups plus Wideband.
Note, we don`t actually sell the Yagi 18 wideband (because the DY14WB outperformed
it by a significant margin) but the gain plot is included because it directly compares
aerials of the samemodel. Interestingly these grouped Yagi 18s performed just as
well as grouped XB10s, and since the Yagi 18s are cheaper, have lower wind loading
and are (arguably) more robust in construction, we do stock those. The test methodology,
and points to bear in mind when interpreting the results, are explained above. The
figures are obviously for this particular model of antenna. Other models varied in
performance and this was particularly the case for gain outside the designed for
band. As an example, the point above which significant gain fall off occurred, for
A group aerials this varied from CH40 to CH42, and for B groups from CH56 to CH59.
For gain within band, other tested 18 element A groups (which we don`t stock) gave
around 3dB (av) more than a DM Log, the other B groups gave 4 to 4.5dB and other
C/D groups gave 4 to 4.8dB.

I must confess to some surprise that the Yagi18 K performs as well as it does up
to CH62, but this was consistent over three sets of tests on three different days.
It will be noted that the B group “beats” the K (on average) over the K band. However
this is primarily due to its excellent performance in the B group, note how the B
trounces the Tri Boom (e.g. DAT45), which is a larger and more expensive aerial don`t
forget. The K is superior to everything bar an A group at the bottom of the band,
and this is the area that is the weakest by far for all wideband (or semi wideband)
aerials. Note that the A group antenna is a huge 3.8dB up on the wideband (of the
same size) for the A group frequencies, it`s also a very significant 3.2dB up on
the (larger) Tri Boom antenna. In fact such is the widebands inferiority that there
is no such thing as a “High Gain” wideband aerial for the A group frequencies. The
C/D`s performance was inconsistent, it was sometimes only on a par with the E and
the W/B, but sometimes it was in front ! It would have been easy to “massage” the
results to say what they should, but being supremely honest, I decided not to........

We tested the aerials against each other at the same time, in the same location,
and in actual reception conditions. We have also retested the same antennas and find
the signal reception can vary for no apparent reason (possibly the temperature or
humidity ? ) so our figures are based on more than one test and our own everyday
experience.

In summer 2007 I decided to institute a major new test programme and identified a
site on the hills above Sheffield which would enable me to do this as it has “line
of sight” off four main transmitters and two repeaters. Between them they cover virtually
all the TV band frequencies.

Some of the most significant data concerned the response of grouped antennas above
and below the designed for frequency band, this is particularly relevant for some
transmissions which aren`t within the transmitter`s original (analogue) group. As
an example it proves that a B group aerial (certainly the ones we sell ! ) will work
perfectly well on CH 55, and not too bad on 56 either [see the relevant graph]. Crappy
Contract aerials might not though !

At least two readings were taken - sometimes many more - on every frequency for every
aerial (including many not published on this site), so some idea of the work involved
can be imagined. I reckon I took around 8,000 individual readings, and that was just
the 2007 tests ! Whilst it was very interesting to start with, it could became a
hell of a grind !

But how accurate are these tests ?

Well, I can only say that when I`ve retested aerials, the results, when comparing
similar types of aerial, were pretty much the same, as indeed they are when I`ve
tested the same aerials on the roof of our shop, a completely different location
(and height off the ground).

Furthermore, the results are actually more or less what you`d expect.

The height question.....

Now, when these tests were first published some people said "they`re not valid because
you`re testing aerials only 6ft from the ground". For various reasons (including
the fact the results were more or less the same on our shop roof) I didn`t accept
that argument, but I couldn`t prove I was right, until September 2011......

Whilst retesting a Yagi18A and a XB10A I decided to take a 2x2 bracket and a 6ft
pole* along so I could mount the test aerial on the latter and then slide it from
6ft to 12ft, and back again. I tested them against each other at 6ft, and again at
12ft, then, repeated the process to increase the accuracy.

It`s very important to understand the difference between thereceived signal at the
two heights, andthe difference in the received signalbetween the two aerials at
those heights. The former obviously did vary, and by quite a bit, but the latter
hardly varied at all, even less than I thought it might. On reflection this isn`t
that surprising because testing similar aerials against each other at the same time,
is the most accurate way to test comparative performance.

It should be noted that as antennas leave their designed for band their performance
can become erratic and the further out of band you go the more pronounced this becomes.
This can give spurious readings, particularly in a spot where multiple TXs can be
received, because the aerials directivity can become very poor and inconsistent.
This is the main reason why we have not published some readings (e.g. C/D off an
A group) as they are meaningless.

In order to make the results comparable all readings are in dBuV and are all relative
to a DM Log Periodic aerial. The latter has a pretty flat gain curve and thus is
an ideal control antenna. Quite apart from anything else, wherever possible (i.e.
in reasonable signal areas), Logs should be used as a matter of course, so the table(s)
will show how much gain you have to make your decision on antenna choice. Note how
the Log performs pretty well (in terms of gain) against small/medium wideband Yagis
at the bottom of the band(s) but falls behind as the frequency rises. For those who
are interested I reckon that, conservatively speaking, the gain of a DM log would
be about 6 dB at the bottom of the band, then rising by about one dB in the middle,
before dropping a little at the top end. These are the figures I used when calculating
the absolute gain for the graphs.The absolute gain figures are conservativeestimates,
though they are accurate relative to each other.Remember that all aerial test readings
are approximate anyway, as far as I`m aware no lab will even guarantee accuracy better
than +/- 0.5dB, and relative to each other these test results aren`t going to be
much behind that.

Note this is dBd, gain compared to a half wave dipole, NOT the (dishonest ? ) dBi....

Such are the signals available at 1140ft that even the DM Log gave/gives the signals
shown in the table below. Bear in mind that the Yagi18s were giving up to 7dBμV more
than that and the XB16s up to 9dBμV more, that`s NINE ! Just to put it in perspective,
one should be aiming for 60dBμV (on digital), more than that and cross modulation
interference can result.